The diagnosis of certain congenital heart defects can now be made as early as 12 weeks of gestation due to advances in fetal echocardiography. Fetal cardiac surgery, which has been investigated since the early 1980s, is an increasingly viable solution to prevent simple cardiac lesions from progressing into serious defects requiring major surgery. The most significant obstacle to successful fetal cardiac bypass has been placental dysfunction, causes of which include blood contact with extracorporeal surfaces, priming substances (maternal blood), and increased placental vascular resistance. The goal of this proposal is to develop a novel fetal cardiac bypass circuit capable of delivering pulsatile flow and adequate gas exchange with minimal priming volume. [unreadable] [unreadable]